The strength, fracture, and chemical changes of poly-(p-phenylene benzobisthiazole) after exposure to molten and vapor deposited aluminum

Abstract

The tensile properties, fracture behavior, and surface chemical composition of the rigid-rod heterocyclic aromatic polymer fiber poly-(p-phenylene benzobisthiazole), PBT, have been measured as a function of contact with nominally zero valent aluminum overlayers. The samples were produced by immersion of suitable fiber or film specimens in a molten aluminum-12.7 wt. % silicon alloy or by aluminum-vapor deposition followed by heat treatment. The strength of uncoated PBT fiber was 3.0 GPa. After 5 min immersion in the molten aluminum alloy, strengths drop to 80% and 25% of the uncoated fiber values for 600° and 700 °C immersion, respectively. Fiber strengths after aluminum immersion are from zero to 20% lower than the strength for corresponding uncoated fibers heated at an equivalent temperature in argon. Coated fibers exhibit tensile strengths after heating intermediate to similarly heated uncoated or immersed fibers. For all types of samples, the fiber fracture mode changes from fibrillar at failure strengths >1.9 GPa (independent of the environment) to planar at failure strengths <1.9 GPa. X-ray photoelectron spectroscopy of PBT fiber and film surfaces indicates oxidation of the polymer surface has occurred, most likely during fabrication of the fiber or film. The oxygen content of the surface layer is decreased when the film is immersed in molten aluminum-silicon alloy. The lack of corresponding changes in the relative intensities of the polymer C, S, or N photoemission peaks after this immersion suggests that the surface oxidized layer plays some role in protecting the polymer from degradation by molten aluminum. These results strongly suggest that it is possible to fabricate low-density, high-strength PBT/metal composites by liquid aluminum alloy infiltration if the melt temperature is kept below 680 °C and the contact time with molten aluminum kept below 3 min.

Rigid‐rod polymeric fibers

“…Low compressive strength limits PBO applications. Efforts to improve compressive strength include incorporation of inorganic components to provide lateral support to fibrils,118–120 inducing morphological changes for interfibrillar entanglement,121–123 covalent crosslinking by radiation124 or by heat, as well as the development of intermolecular hydrogen bondable structures. Of the various approaches used, crosslinking91, 97 and hydrogen bonding125 appear to be most promising.…”

Rigid‐Rod Polymers: Synthesis, Processing, Simulation, Structure, and Properties

“…Even at 450 °C, PBZT film was found to retain its room temperature ultimate strength 176. PBZT fiber lost only 20% of its original strength after 5 min immersion in molten aluminum alloy at 600 °C 177. Similarly, at 400 °C PBO fiber retains 74% of its room temperature modulus 178…”

“…It has been suggested187,196 that a matrix material infiltrated within the fiber may provide lateral support to the fibrils. In consideration of the high compressive strength of inorganic fibers such as glass or alumina fibers, the attempt177,200–203 has been made to incorporate these inorganic components into PBO and PBZT fibers and films via coating or infiltration in order to improve the compressive behavior. While no significant improvement in compressive strength was observed204 upon exposure of reactive resin‐infiltrated PBO fibers to irradiation, a slight increase (≈13%) in compressive strength, as well as an increase in tensile strength and elongation to break, was reported205 when Kevlar fibers were infiltrated with thermosetting epoxides, novolac, or bismaleimides.…”

Preparation and characterization of nanocomposites of poly-p-phenylene benzobisthiazole with graphene nanosheets

“…31,32 As-extruded PBT lms possess tensile modulus of 240 GPa and tensile strength of 1.5 GPa, 33 and exhibits high thermal stability up to 600 C in nitrogen. 34 Although the PBT backbones consist of extended p-conjugation that could facilitate the movement of charge carriers, PBT polymer is a insulating material with conductivity of < 10 À12 S cm À1 at room temperature. 35 However, there are very limited works on improvement of its electrical and electronic properties.…”